In Japan, the output of unused biomass resources, that is, cellulose-type industrial (general) waste materials, such as forest thinnings, construction waste materials, rice straw and rice husk, as well as old paper and waste paper, reaches up to 50 million tons per year. Use of these biomasses as an energy source is considered to be “carbon-neutral” because they do not upset the global CO2 balance, and the biomasses are highly expected as an energy source that contributes to the greenhouse gas reduction. Under such circumstances, it has been suggested and studied to produce ethanol as a biofuel from unused cellulose-type or lignocellulose-type biomass resources and to use the produced bioethanol as a raw material for the syntheses of oxygen-containing compounds for addition to gasoline or chemical products, or as regional heat source and electric power source.
However, there are no fermentative bacteria available in nature, which produce ethanol by directly degrading and fermenting cellulose-type or lignocellulose-type biomass resources. Therefore, it is expected to create a fermentative bacterium capable of fermenting and converting cellulose partial degradation products (cellooligosaccharides), xylose and mannose present as a mixture in an acid-treated saccharified solution of celluloses and hemicelluloses simultaneously into ethanol by using metabolic engineering technologies and cell surface presentation technologies. It is also expected to construct an innovative energy-saving high-efficiency conversion process, wherein a continuous fermentation apparatus having a bred fermentative bacterial strain as a catalyst element is incorporated.
The present inventors previously succeeded in the creation of a transformed microorganism capable of producing ethanol from a pentose by introducing a foreign gene encoding at least one enzyme selected from a xylose isomerase, a xylulokinase, a transaldolase and a transketolase into a microorganism of the genus Zymobacter incapable of assimilating a pentose (Patent Document 1). For the purpose of efficient production of ethanol from a raw material containing mannose, the present inventors also succeeded in the creation of a recombinant microorganism by integrating a foreign gene encoding a phosphomannose isomerase into the chromosome of a bacterium of the genus Zymomonas to give stable mannose fermentation capacity to the bacterium (Patent Document 2).    Patent Document 1: JP 2005-261421 A    Patent Document 2: JP 2007-14306 A